The PS Vita will have some unique features, some derived from the Xbox 360, such as “custom soundtrack” in games. This is because of the three cores that power the handheld, which allows it to run a few processes simultaneous to playing a game, though one thing it won’t be able to do on launch is allow you switch between the Web Browser and a game, without first exiting the game.
Impress Watch, A Japanese gaming site had to make a correction to their site after they wrote that the browser would indeed be accessible while in a game, SCE contacted them to correct this. It seems that one core of the CPU is dedicated to the OS, one is dedicated to the game and one is used for playing music and accessing Twitter, but the web browser will also require a dedicated CPU, the same one used for games, so don’t expect to be able to look for hints on the fly while playing Uncharted.
There is a possibility that this will be patched shortly after launch, but there has been no conformation of that. I find this most surprising because the 3DS, a far less powerful system, can do just that–use the browser without exiting the game.